1. Field of the Invention
The present invention relates to an opening system of a door-type cassette holder, and more particularly to a cassette holder opening system having a damper, the damping force of which varies according to the opened angle of a cassette holder.
2. Prior Art
A cassette holder 2 of door type as shown in FIG. 1, which is opened by the spring force of a spring 6, is used for a holder for receiving a tape cassette in a cassette player such as a camcorder, etc.
In the cassette holder 2, an impact or noise can be generated due to the abrupt opening of holder 2 when holder 2 is opened by the spring force of spring 6, the cassette or the holder may be broken easily and users may feel unpleasant in using the cassette. Therefore, highly required is a damper which can damp the impact or noise due to the abrupt opening of cassette holder 2 in opening cassette holder 2.
FIGS. 2 and 3 show a cassette holder opening system having a damper to meet the above-described requirement.
A damper 3 disposed in a cassette holder 2, as shown in FIG. 3, comprises an upper and lower cover 32 and 34, which are combined together to form a space therein. In the space between upper and lower cover 32 and 34, viscous liquid 37 is filled, and a first and second ring 38 and 39 are disposed to prevent leakage of viscous liquid 37. A rotation fan 35 is disposed rotatably at lower case 34 in such a manner to be immersed in viscous liquid 37 in the space so that viscous resistance is applied to the rotation thereof by viscous liquid 37.
Lower case 34 of damper 3 includes locking hooks 33 which are engaged with locking holes 13 of the cassette holder 2.
A sector gear 22 is formed at frame 4 in which a rolling gear 25 is engaged. A boss 36, one end of which is fixed to rotation fan 35, extends through upper case 32 and an opening 16 formed at cassette holder 2, which are coaxial with each other, to be fixed to rolling gear 25.
Meanwhile, spring 6 is disposed between cassette holder 2 and frame 4 to connect them with each other, and cassette holder 2 is pivotally attached to frame 4 by a hinge pin 5.
In a conventional cassette holder opening system having damper 3 of the above construction, spring 6 is elongated when cassette holder 2 is closed, and thereby a biasing force to open the cassette holder is applied to the cassette holder 2 by the spring force of the elongated spring 6. According as cassette holder 2 is opened, rolling gear 25 rolls upwards along sector gear 22. In this case, the rotation of rotation fan 35 is resisted by the viscous resistance of viscous liquid 37, so that the spring force of spring 6 is damped, and thereby the impact and noise due to the abrupt opening of cassette holder 2 are reduced.
Meanwhile, because one end of spring 6 is attached to frame 4 and the other end thereof is attached to cassette holder 2, the length of spring 6 is changed according to the opened angle of cassette holder 2, as shown in FIG. 2.
That is, the length of spring 6 becomes shorter according as the opened angle of cassette holder 2 becomes larger. In this case, because the spring force of spring 3 is proportional with the elongated length of spring 3, the spring force is reduced according as cassette holder 2 is opened. While, according as the opened angle of holder 2 increases, the opening velocity of holder 2 gradually increases due to the acceleration, so that damper 3 exhibits a gradually increasing damping force.
Therefore, though the abrupt opening of cassette holder 2 can be prevented by damping the opening of cassette holder 2 by damper 3, holder 2 is intermittently stopped in the course of being opened. Further, the spring force to open the cassette holder by spring 6 may be smaller than the damping force of damper 3 in the terminal stage of opening cassette holder 2, and thereby cassette holder 2 may not be opened completely.
Moreover, because damper 3 must be filled with viscous liquid 37 of gel state, the injection of the viscous liquid and the manufacture and maintenance of the damper are difficult, and the manufacturing cost thereof is increased due to the complicated construction thereof.
Meanwhile, U.S. Pat. No. 4,159,495 issued to Tsutsumi discloses an opening and closing device for cassette holder, which is adapted to damp any shock caused during opening operation of the cassette holder and at the same time to prevent occurrence of unpleasant shock noise. The opening and closing device for cassette holder comprises cooperating members in cooperation with an object to be opened and closed, a locking member for locking the cooperating members in the closed state of the object, and a rotative member for exerting damping effect on the object during opening and closing operation thereof by way of following the movement of the cooperating members.
However, the opening and closing device for cassette holder having the above construction requires a complicated mechanism consisting of separate members such as cooperating members, a locking member, and a rotative member, thereby the manufacture of the device is difficult and the manufacturing cost thereof is expensive.